Datasheet

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AM Discovery
TPS23841
SLUS745A – NOVEMBER 2006 – REVISED MAY 2007
AUTO MODE FUNCTIONAL DESCRIPTION (continued)
The TPS23841 uses a four-point measurement technique using two low level probe signals (typically 4.4 V and
8.8V) during the discovery process to determine whether a valid PD is present. The use of a multipoint detection
method for the PD resistor measurement allows accurate detection even when series steering diodes are
present. The low level probe voltages also prevent damage to non-802.3 devices. When a valid PD has been
detected the TPS23841 moves to classification. If a valid PD has not been detected the TPS23841 continues to
cycle through the discovery process. The waveform in Figure 2 shows typical N-pin waveforms for the discovery
of a valid PD and the failure to discovery due to a discovery resistor of 15 k Ω and 33k Ω .
Figure 2.
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